[squeak-dev] enabling read-only literals...

Eliot Miranda eliot.miranda at gmail.com
Wed Mar 11 22:38:23 UTC 2020

Hi Nicolas,

On Wed, Mar 11, 2020 at 2:35 PM Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

> Hi Eliot,
> IMO you can proceed, it's better to introduce this kind of changes in
> early stages of the release cycle.
> Anyway, it's 6.0, not 5.x ;)
> Once upon a time, I did purposely use mutable literal array as shared
> state with a scope local to single method (that is without leaking the
> scope thru a class var).
> It's possible I also saw that trick once or twice, but its really an abuse
> of undocumented and implementation defined behavior.
> Anyway, we can decide to later add a defaultAction or better let that
> responsibility to "clients" unwilling to change their code.
> IMO, we should start gathering release notes about those important
> changes, otherwise it's a lot of work that we postpone to the release team.

That's a really good idea.  I'm going to crate a class-side method in
Object class documentation that will be a release nots scratch pad.  We can
delete it as we approach the final release.

> Le mer. 11 mars 2020 à 22:10, Eliot Miranda <eliot.miranda at gmail.com> a
> écrit :
>> Hi All,
>>     I'v committed the core support for read-only objects, adapted from
>> Clément's Pharo implementation.  Enabling read-only literals is a very
>> small step from that (three methods modified in the parser, and one method
>> modified in Symbol class).  I would like to do this as soon as possible,
>> but it may break code.  Hence my asking for permission/sending out a
>> warning before hand.  Note that the only code it will break is bad code;
>> code that writes to literals.
>> With the changes installed doing this:
>> #(1 2 3) at: 2 put: 'nevermore'
>> raises a ModificationForbidden exception with the message text
>> "ModificationForbidden:  #(1 2 3) is read-only, hence its field 2 cannot be
>> modified with 'nevermore'"
>> When we added read-only object support to VisualWorks some of the
>> engineering staff were of the opinion that insulating customers from the
>> change was a necessary thing, and so we implemented a preference to allow
>> automatic mutating of read-only literals so that customers whose code did
>> modify literals could set the preference rather than fix their code.  I
>> *really* don't ant to do this.  It is a lot of complication for little
>> gain; the right fix is just to rewrite the code not to write to literals.
>> Note that that's as easy as:
>> #(1 2 3) copy at: 2 put: 'nevermore'; yourself
>> =>
>> #(1 'nevermore' 3)
>> since copies of read-only objects are mutable.
>> So do I have everyone's consent in changing trunk over to read-only
>> literals?  If there are no strenuous complaints by tomorrow noon, PST, I
>> shall effect the change.
>> To avoid recompiling (which can produce unbound methods, etc) I shall
>> change literals to be read-only via a pass over all literals and a pass
>> over the Symbol table.  Hence the change should be non-invasive.  If your
>> code (like probably 99.9% of all code in the system) doesn't write to
>> literals you won't notice.
>> _,,,^..^,,,_
>> best, Eliot

best, Eliot
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